Microelectronic imagers are used in digital cameras, wireless devices with picture capabilities, and many other applications. Cellular telephones, Personal Digital Assistants (PDAs), computers, and stand alone cameras, for example, are incorporating microelectronic imagers for capturing and sending pictures. The growth rate of microelectronic imagers has been steadily increasing as they become smaller and produce better images with higher resolution.
Microelectronic imagers include image sensors that use Charged Coupled Device (CCD) systems, Complementary Metal-Oxide Semiconductor (CMOS) systems or other imager technology. CCD image sensors have been widely used in digital cameras and other applications. CMOS image sensors are quickly becoming very popular because they have low production costs, high yields, and small sizes.
One problem which occurs as image sensor pixel sizes decrease is an increase in optical crosstalk. Optical crosstalk occurs when light intended for a particular photodetector misses that photodetector and strikes a neighboring photodetector, thereby contaminating the adjacent pixel's charge packet with light intended for another pixel. Sensors often cover photodetectors with a color filter array, e.g., a Bayer filter pattern array, having filter elements so that colored light may be sensed by the photodetectors. While optical crosstalk may be caused by numerous factors, two contributors to optical crosstalk are particularly important with respect to embodiments disclosed herein. These include the deflected photon, and the errant photon.
The first contributor to optical crosstalk, the deflected photon, occurs when a photon intersects the intended filter element at an angle and winds up striking a conductor in a metallization layer. The photon, after striking the metallization layer, is deflected to an unintended photodetector. Thus, instead of going through the intended filter element and entering the intended photodetector, the photon, due to metallization layer deflection, enters an adjacent pixel's photodetector. Failure of a photon to enter the intended photodetector results in the adjacent pixel's charge packet being contaminated.
The second contributor to optical crosstalk, the errant photon, occurs when a photon is off course without even being deflected by a metallization layer. In these cases, a photon intersects the intended filter element at a substantial enough angle to cause the photon to go through a color filter which is not associated with the photodetector the photon will eventually impact. These photons are not deflected by a metallization layer, yet still enter an unintended photodetector and contaminate that pixel's charge packet.